Why Chameleons can change colour?

One day, a chameleon was resting under a coconut tree when he saw a woodpecker flying hurriedly towards him.

"what's the matter?" asked the chameleon. "A forest fire has broken out, come on, we're flying to another forest." explained the woodpecker. "Foxie the fox wants to eat me, so I can't come with you," said the chameleon. Then the woodpecker gave the chameleon a vile of liquid labelled 'colour-changing liquid' and said, "drink this and you will be able to change your colour" (that time chameleons were only green in colour). When the chameleon drank the liquid he became light brown, blending with the dried grass.

From that day onwards all chameleons were able to change colour and blend with the surroundings.

This is called 'Adaption for Survival'.